Process in continuous extrusion of metals and the like

ABSTRACT

Metal and the like is extruded by means of a screw press including a power zone and extrusion die means. On leaving the power zone, the metal is heated to facilitate its passage from the screw to and through the die means.

ilited States atent Runevall et ai.

[ 1 Sept. 26, 1972 1 PROCESS IN CONTINUOUS EXTRUSION 0F METALS AND THE LIKE [22] Filed: Nov. 12, 1970 [21] Appl. No; 88,707

[30] Foreign Application Priority Data Nov. 17, 1969 Sweden ..l57lO/69 52 US. Cl ..72/262 0 51 Int.Cl ..B21c29/00 [58] Field of Search ..72/262;'-18/30,SM

[56] References Cited UNITED STATES PATENTS 2,743,812 5/1956 Ljungberg ..72/262 2,593,265 4/1952 Chase et a1. ..72/262 3,055,053 9/1962 Livingston et a1 1 8/30 SM 2,172,651 9/1939 Dunsheath ..72/262 Primary ExaminerRichard J. Herbst Att0rneySommers & Young 5 7 ABSTRACT Metal and the like is extruded by means of a screw press including a power zone and extrusion die means. On leaving the power zone, the metal is heated to facilitate its passage from the screw to and through the die means.

5 Claims, 9 Drawing Figures PATENTEDSEP26 m2 3.333.394

sum 2 [IF 3 0 I 100 200 I 300C A Jamey PATENTEDSEPZB I972 SHEET 3 [IF 3 PROCESS IN CONTINUOUS EXTRUSION OF METALS AND THE LIKE BACKGROUND OF THE INVENTION The present invention relates to a process for the continuous extrusion of metals and the like by means of screw presses.

During the extrusion of metals, for instance lead, by means of a screw press considerable pressure is necessary to force the lead through the die block and the dies of the press. On account of the fact that a pressure at a couple of thousand atmospheres is required, the friction losses in the die block will be considerable. This applies to the sliding frictions between lead and the steel faces of the screw and the die block respectively, as well as to the internal friction losses within the lead itself, when this is reshaped in the press head and in the dies. The friction losses which are taken from the kinetic energy of the metal cause the pressure to be reduced towards the dies, whereby the efficiency of the machine is limited. Furthermore this has the effect that the usability of such a screw press will be strongly reduced with respect to hard lead alloys or other hard metals such as aluminum. I

The processes thus far known for extrusion of metal and the like have not been entirely successful in eliminating the above disadvantages. Thus it is the object of the present invention to achieve an improved process for continuous extrusion, which has a better efficiency and a wider field of application than previously known processes.

SUMMARY OF THE INVENTION In the process of the invention metals and the like are extruded continuously by means of screw presses. In their power zones the rotational energy of the screw is transferred to the metal in the form of high pressure and an axial forward movementof the metal. The advantages of the invention are achieved by causing the metal, as soon as possible after it has left the power, to be heated whereby internal friction in the lead is reduced by the elevated temperature. This reduction in friction makes the passage of the metal from the screw tip to the shaping dies easier. The metal can be heated by supplying electric heat, hot gas or liquid or combustion gases in theinterior of the screw tip and/or in a wedge-shaped member dividing the lead and located immediately above the tip of the screw.

According to another embodiment of the invention, the heating can be achieved by means of inner friction in the metal mass itself. The threads of the top of the screw are, for this purpose, shaped so that they constantly knead the metal mass during the rotation of the screw.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described more in detail below with reference to the accompanying drawings, in which:

FIG. 1 shows a known screw press for extruding lead tubes;

FIG. 2 is a side view of a lead dividing member located in the die block of the screw press in FIG. 1;

FIG. 3 is a section along the line 3-3 of FIG. 2;

FIG. 4 is a section along the line 4-4 of FIG. 2;

FIG. 5 is a graph showing the shearing strength as a function of the temperature of pure lead (A) and of a lead alloy (B);

FIG. 6A-6D inclusive show some possible designs of the screw tip of the press which operate to knead the metal mass according to an embodiment of the invention, FIGS. 68 and 6D being plan view of the screw structures shown in FIGS. 6A and 6C respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a known screw press for extrusion of a lead tube with a screw 2 located in a screw housing 4, whose interior walls are provided with longitudinal grooves (not shown). Molten lead is supplied through an inlet 3, and while being cooled the lead is moved upwards due to the rotary motion of the screw 2. When the lead has been cooled below its melting point, it enters during its motion upwards the so-called power zone of the screw press, which is the zone where the lead is further cooled and in which the pressure in the solid lead mass is built up, and in which the rotational energy of the screw is thus transferred to the lead mass in the form of high pressure and upward motion of the lead. The lead mass is moved further upwards, is divided by a lead dividing member 9 located in a die block 5 and is extruded through dies 6 and 7 to form a pipe 8. The lead dividing member 9 is shown in detail in FIG. 2, 3 and 4. The rotational energy of the screw will thus be transferred to this solid nut and the nut is forced upwards.

The pressure necessary for the extrusion is thus built up in the power zone of the screw press, in which a strong nut of solid lead is formed around the screw in order that great energy might be transferred to the lead mass via the nut.

The energy which can be transferred to the nut from the screw depends on the temperature of the lead. In FIG. 5 the curve A shows the shearing strength of pure lead depending on the temperature, and the curve B relates to a lead alloy. Obviously the temperature of the lead in the power zone, where the nut is formed, should be as low as possible.

The amounts of energy which are converted in a normal I-Iansson-Robertson lead press, during extrusion of tubes, will be better appreciated by reference to the following table:

Pure lead Alloyed lead 40 kg 20 kg 40 kW 20 kW For coolingtin the power zone of the press) of the lead to solidification and about C it is necessary to remove from the lead approx.

For extrusion the screw has to (in the power zone) trans- 5 fer to the lead an effect of strength of the nut formed by the lead in the power zone is secured.

During the passage of the lead mass from the power zone through the die block to the from dies, large losses of energy in the form of friction arise. in the process of the invention these shearing are reduced by heating the lead after it has left the power zone. As appears form FIG. 5, the shearing strength is considerably reduced in this way and consequently also the inner friction. If the inner friction and the pressure needed for extrusion of the lead is thus reduced, the friction losses between the lead and the steel parts of the die block are also reduced.

The heat can be supplied to the lead for instance in the form of electric heat, hot gas or liquid, or combustion gases in the interior of the screw tip 2 and/or the lead dividing member 9. No example of this is shown on the drawings.

The heat may also be supplied to the lead in the form of friction heat. The upper threads of the screw tip above the power zone may be provided with irregularities which, during the rotation of the screw while the threads carry the lead upwards, knead the lead so that it is heated through internal and/or external friction. FIGS. 6A-B and 6C-D, respectively, show two examples of such thread configurations the uppermost thread of the screw tip being provided with cuttings and oblique grooves on the edge of the thread. These cuttings and grooves are shaped so that metal does not accumulate therein. Accumulation of metal should be avoided especially at extrusion of alloys, as a segregation of the alloying components may arise in a remaining metal quantity, which might later be carried along and cause quality errors in the extruded metal product. It is advantageous if the screw tip is so designed that the lead is here reshaped and kneaded in such way that the heating is substantially achieved by internal friction in the whole lead mass and not through surface friction between lead and screw, which might easily cause concentration of alloying components where the alloy is rubbed against steel.

Another advantage of heating by means of kneading from the rotating screw, is that such heating is direct proportional to the speed of the screw and thus also proportional to the extruded quantity of lead, and the heating ceases automatically when the machine is stopped.

This way of improving the extruding ability of screw presses can of course with advantage also be used for such screw presses which lack a die'block, but instead have inner dies placed in a spider which centers the inner die in the outer die. The spokes of such a spider offer a resistance corresponding to the resistance of a die block, such as shown in FIG. 1.

Thanks to the heating the lead will flow easier through the complicated nooks in the die block towards the shaping dies. There it may, however, be

suitabl to cool t e lead ain ccord'n to know metho s so that if, by col wor ing, is given good mechanical properties at the very moment of extrusion.

With reference to FIG. 5 it has been mentioned that the internal friction of lead and lead alloys is strongly dependent on the temperature of the lead. Investigations show, however, that the sliding friction metal/steel is not so strongly dependent on the temperature or on the kind of alloy being used. It is, however, emphasized that if the internal friction is reduced with the process of the invention, it will be possible to operate with a lower pressure, and then the friction between steel and metal will also be reduced, as this sliding friction metal to steel is proportional to the pressure.

What we claim is:

l. A process for the extrusion of metal and the like by means of a screw press having a power zone in which the rotational energy of the screw is transferred to the metal in the form of pressure and axial forward motion, comprising the step of heating the metal as soon as possible after it has left the power zone, whereby the friction between the metal and screw is reduced by the increased temperature of said metal to facilitate the passage of the metal from the screw to and through the dies which shape the extruded product, said metal heating step being effected by reshaping and kneading the metal at the tip of the screw downstream of said power zone to produce heat in the form of internal friction within the metal.

2. The process of claim 1 wherein the internal friction in the metal mass is achieved by shaping the threads of the screw at the screw tip so that, during the rotation of the screw, said shaped threads constantly reshape and knead the metal mass.

3. The process of claim 1 wherein said kneading is achieved by means of depressions and/or enlargements on the core or threads of the screw tip.

4. The process of claim 2 wherein the friction heat produced at the screw tip is carried away by means of a coolant flowing within the screw.

5. The process of claim 3 wherein the depressions and/or enlargements on the threads or core of the screw are even in configuration, streamlined, and so directed that the metal cannot accumulate and remain therein. 

1. A process for the extrusion of metal and the like by means of a screw press having a power zone in which the rotational energy of the screw is transferred to the metal in the form of pressure and axial forward motion, comprising the step of heating the metal as soon as possible after it has left the power zone, whereby the friction between the metal and screw is reduced by the increased temperature of said metal to facilitate the passage of the metal from the screw to and through the dies which shape the extruded product, said metal heating step being effected by reshaping and kneading the metal at the tip of the screw downstream of said power zone to produce heat in the form of internal friction within the metal.
 2. The process of claim 1 wherein the internal friction in the metal mass is achieved by shaping the threads of the screw at the screw tip so that, during the rotation of the screw, said shaped threads constantly reshape and knead the metal mass.
 3. The process of claim 1 wherein said kneading is achieved by means of depressions and/or enlargements on the core or threads of the screw tip.
 4. The process of claim 2 wherein the friction heat produced at the screw tip is carried away by means of a cOolant flowing within the screw.
 5. The process of claim 3 wherein the depressions and/or enlargements on the threads or core of the screw are even in configuration, streamlined, and so directed that the metal cannot accumulate and remain therein. 